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Consuming vanquished enemies' mana had little to do with the underlying reason for Maori cannibalism, a new book by historian Paul Moon says.

Instead cannibalism, pre-colonialism, was simply about "rage and humiliation", he says in a book to be released next month.

This Horrid Practice is the title borrowed from Captain James Cook's journal entries on the topic during his expeditions here. While he largely treated the practice without sensationalism, there has been a paucity of academic work on the subject in New Zealand _ Moon's book is the first.

Drawing on journals and letters from first Maori/European encounters, Moon says generations have swallowed the mana argument. However, the first time it appeared was in the 1850s _ the decade in which Maori and Pakeha populations evened up and Maori were becoming more influenced by colonial ideas.

With engagement with Anglican and Catholic Churches, Maori were starting to feel shame at cannibalism, alongside a desire to reshape or excuse past behaviour, Moon said.

"They thought, `Well Christianity has the communion which is symbolic cannibalism where the bread and the wine become the flesh and blood of Christ'. You consume it and you consume your god, so really, it's a grafting of Christian ideas on to traditional cannibalism. Therefore, you consume your enemy, you consume their mana."

But it wasn't just Maori engaging in excuse making, some in the academic fraternity, influenced by the idea of the "noble savage" have also been complicit in it, he said.

"Academics wish to sanitise aspects of indigenous culture where everything is kind of pure in the garden of indigenous cultures."

Other reasons why he believes the argument doesn't hold up is that mana wasn't bio-cumulative, you couldn't get more by eating more people. The idea of "mauri" or life force leaving the body when someone died meant it didn't make sense that mana could be stored in flesh and bones.

He believes high levels of stress caused by high expectation of violence, passed through the generations, was the underlying reason for cannibalism.

The book is released on August 4.